drivers: spi: gecko: add new driver for SPI communication via EUSART

Added a new driver to support SPI communication via EUSART. Since the
Silabs EFR32MG24 family SoCs have only one USART, EUSART support is
necessary for implementing SPI functionality.

Signed-off-by: Teresa Zepeda Ventura <teresa.zvent@gmail.com>
10 files changed